Hardening treatment of high-frequency induction heating equipment tubes?

Hardening treatment of high-frequency induction heating equipment tubes?

  The purpose of hardening is to increase the vacuum of some tubes with reduced vacuum. Return to normal performance. It is impossible to repair the electronic tube with air leakage caused by poor manufacturing process (that is, the infiltration of outside air into the tube). The object of hardening treatment refers to the tube whose vacuum degree is reduced due to the long storage time.

  Generally, metals contain trace amounts of gas. When the electronic tube manufacturer evacuates the exhaust body of the electronic tube, it is impossible to exhaust the gas in the electrode. During long-term storage, the residual gas in the metal electrode will be released. Hardening can be used to restore the vacuum of the tube. Before hardening, it is necessary to clarify the use conditions of the tube to determine the anode power loss that the tube can withstand. Each type of electronic tube has a specified limit dissipation power Pam, such as Pam=60KW of FU-433S and Pam=5KW of FU-89F.

  But these are the data given under the specified cooling conditions. For example, for FU-433S, the flow rate of anode cooling water is required to be no less than 90L/min; for FU-89F, the anode cooling air is required to be no less than 850m3/h. If the cooling conditions of the anode cannot meet the requirements, the Pam will also be reduced. At present, many equipments work under the condition of insufficient cooling, and attention must be paid to it. Hardening can be carried out on high-frequency equipment, and there are two hardening methods, dynamic and static.

  ①In the process of heating the filament, the getter near the filament will play a role after heating, and the inside of the absorbing tube will increase to the rated voltage after ten minutes. of residual gas. The heating time of the filament is determined by the storage time, and the heating time is 0.5h if the storage time is within one year. If the storage time exceeds one year, heat for 1-2h.

  The second step is to connect the tube into a diode (it is reasonable to connect the grid and the filament to make a diode, but practice has proved that this connection method is sometimes feasible, sometimes not feasible, it seems that the tube produces ultra-high frequency parasitic oscillation, a Give the upper positive voltage - even if the positive voltage is very low and only 2~3KV, a large positive current will be generated, causing overcurrent tripping. When this happens, only the grid is suspended and nothing is connected. ).

  At the same time disconnect the anode to the DC blocking capacitor, then from o. 2-0.3 The rated positive pressure begins to gradually increase the positive pressure. During hardening treatment, the power loss of the anode should not be too large. Generally, it is better not to exceed 70% of Pam. For example, the FU-433S pipe should not exceed 60KW×0.7=42KW (as mentioned earlier, if the anode cooling water flow is insufficient, it should be proportionally decreasing). According to the characteristics of FU-433S, when the grid voltage is zero and the anode voltage is 10KV, the anode current is 4A. At this time, the loss power of the anode is Pn=En·Ia=40KW, which should not be increased. If you want to increase the positive voltage, you must add a negative voltage to the grid (the connection method is shown in Figure 2-1) to control the positive current, and do not make Pa more than 42KW. Anode current control For anode power supply used for hardening treatment, it should be a rectifier power supply with a small pulsation coefficient (such as silicon stack rectification, induction voltage regulator voltage regulation).

  ②Dynamic hardening Dynamic hardening is to gradually increase the positive pressure of the tube in the oscillating state. This method does not need to change the circuit of the device, but only requires that the positive pressure can be adjusted from zero to the rated value. At the same time, a load should be connected to the output end of the quenching (or welding) transformer. Because the hardening time may be very long, the dummy load made of water-through iron cans is used.

  Dynamic hardening does not need to add control negative pressure on the grid, which is more convenient. Its anode power loss Pa can be measured by the thermal power equivalent method, or it can be roughly estimated by the following formula: When the oscillator is in normal working state, Pa=E a×Inc×0.35. When a new tube is used and it is found that the positive voltage cannot be increased to the rated value (set this tube as FU-23S, when the positive voltage rises to 10KV, the tube will flash and discharge, causing an overcurrent trip), and the tube will be hardened. It is possible to return to normal.

  When the tube is hardened, the positive pressure can be increased from 9KV, with 500V as a gear, and each gear stays for 10 to 15 minutes. For example, when the positive pressure rises to a certain value, a light blue glow appears in the glass bulb of the electronic tube. After a period of stability, the blue light has disappeared or become weak, and the positive pressure can be increased again. If the positive voltage rises to a certain value, the positive current rises sharply, and the overcurrent trips, the positive voltage should be lowered by one gear, and the voltage should be increased after 20-30 minutes of stabilization until the rated voltage can be added.